Fabrication of hybrid metal/metal curved composite profiles using differential velocity sideways extrusion process

Hybrid metal/metal composites are attracting great attention globally for low-carbon manufacturing because they can be ultra-light and have a good combination of mechanical and other desired properties. The application of hybrid metal/metal curved composite profiles to replace traditional curved sections can give full play to the advantages of composite materials. To examine the feasibility of forming such profiles, an aluminium/magnesium metal hybrid curved section was manufactured using a newly developed differential velocity sideways extrusion (DVSE) process. A bimetallic billet comprising a magnesium cylinder enclosed by an aluminium tube was extruded using different speed settings on the two extrusion punches to give precisely controlled radii of curvature in the product. The mechanics of deformation were studied using practical experiments and process modelling, and the microstructural and mechanical properties of the extruded section were determined. It has been demonstrated that the DVSE process with appropriately chosen punch speed settings transforms an initially straight billet with its magnesium core and aluminium cladding into a curved extrudate comprising two discrete magnesium cores surrounded well by aluminium, with a harder surface layer. A monotonic relationship is found between the curvature and the ratio between the speeds of the two punches. The DVSE process induces grain refinement in both the aluminium and magnesium layers with respect to the initial billet. In the aluminium layers, continuous dynamic recrystallisation is the dominant grain refinement mechanism, whereas in the magnesium layers, the fine grains are {101¯2} tension twins. The present study shows the potential of the novel DVSE process for the production of variable-curvature hybrid metal/metal composites with a good combination of desired properties.